Conventionally, a styrene-acrylonitrile copolymer resin (hereinafter occasionally described as “SAN”) has been manufactured on an industrial scale. This SAN is manufactured in a continuous manner for reasons of improvement in productivity or the like.
On the other hand, the SAN is manufactured by the copolymerization reaction of styrene and acrylonitrile served as raw materials, and this copolymerization reaction is an exothermic reaction. Accordingly, there arises the need to remove the heat of polymerization, in order to continuously manufacture the SAN in a stable manner. Hence, as an apparatus for manufacturing this SAN, there has been proposed an apparatus including a spatial area within a polymerization vessel whereby the heat of polymerization is removed by evaporating part of a polymerization solution into this spatial area.
Incidentally, this SAN has the characteristic of being superior in transparency. However, this transparency degrades as the SAN becomes cloudy if composition of the SAN, i.e., styrene and acrylonitrile components in the SAN, differ in weight ratio. Accordingly, in order to obtain a SAN superior in transparency, it is necessary to uniformize the composition and temperature of a polymerization solution within the polymerization vessel.
However, in a manufacturing apparatus including a spatial area within a polymerization vessel, as described above, whereby heat is removed as latent heat, the composition of an evaporated monomer, solvent and the like and the composition thereof in a polymerization solution differ from each other. If this vapor is condensed and fed back into the polymerization vessel, there arises a portion where the composition of these components in the polymerization solution differs. In addition, operational factors, such as pressure, temperature and a liquid level, interfere with each other in this apparatus and, therefore, vary constantly. Consequently, a residence time and a polymerization ratio vary, thus making it difficult to keep constant the residence time and the polymerization ratio. As a result, the composition of a SAN produced by copolymerization reaction becomes nonuniform, thereby impairing the transparency of the SAN.
Hence, there has been conventionally proposed a manufacturing apparatus including a cooler whereby the heat of polymerization is removed by the cooler.
Japanese Patent Publication No. 47-610 discloses a manufacturing apparatus including a cooling apparatus within a polymerization vessel whereby the heat of polymerization is removed by the cooling apparatus. This manufacturing apparatus has the characteristic that there is no need to provide a spatial area within the polymerization vessel. Consequently, it is possible to keep constant the residence time of a polymerization solution within the polymerization vessel by keeping constant a raw material feed rate. In addition, the manufacturing apparatus has the advantage that there is no need to consider a change in composition due to the condensation of a vapor component.
Japanese Patent Publication No. 55-35912 discloses an externally-attached heat removal apparatus (cooler) capable of scraping the inner wall of a tube. A cooling medium having the temperature of which is lower than polymerization temperature by 5° C. or more but not more than 40° C., flows through the shell of this heat removal apparatus (cooler). By retrieving the polymerization solution out of a polymerization vessel using a pump and introducing the solution into a tube within this heat removal apparatus, heat exchange is made to take place between the polymerization solution and the cooling medium, thereby cooling the polymerization solution. After this, the polymerization solution is once again fed back into the polymerization vessel to remove the heat of polymerization within the polymerization vessel.
Japanese Patent Publication No. 48-29628 discloses a manufacturing apparatus including a polymerization vessel having in the lower part thereof an auxiliary agitating blade composed of a turbine-type agitating blade and a screw-type agitating blade and having in the inner part thereof a cooler.